Tap-changing transformer system including vacuum switch units

ABSTRACT

A TAP-CHANGING TRANSFORMER AND A METHOD FOR OPERATING THE SAME. THE TAP-CHANGING OPERATIONS ARE PERFORMED BY A PAIR OF CHANGEOVER SWITCHES BOTH CONNECTED TO EACH OF A PAIR OF CONTIGUOUS TAPS OF A TAPPED TRANSFORMER WINDING AND BY A PAIR OF VACUUM SWITCH UNITS. THE COMBINATION OF THE AFOREMENTIONED CHANGEOVER SWITCHES AND VACUUM SWITCH UNITS MINIMIZES THE POWER REQUIREMENTS FOR PERFORMING TAP-CHANGING OPERATIONS. THE CHANGEOVER SWITCHES AND THE VACUUM SWITCH UNITS ARE OPERATED BY A COMMON DRIVE WHICH POSITIVELY IMPOSES UPON THE VARIOUS SWITCHING MEANS THE REQUIRED SEQUENCE OF OPERATIONS.

Jan. 12, 1971 A. BLEIBTREU TAP-CHANGING TRANSFORMER SYSTEM INCLUDING VACUUM SWITCH UNITS Filed June 16, 1969 2 Sheets-Sheet l Jan. 12, 1971 A. BLEIBTREU TAP-CHANGING TRANSFORMER SYSTEM INCLUDING VACUUM SWITCH UNITS Filed June 16, 1969 2 Sheets-Sheet :2

United States Patent 3,555,404 TAP-CHANGING TRANSFORMER SYSTEM INCLUDING VACUUM SWITCH UNITS Alexander Bleibtreu, Regensburg, Germany, assignor to Maschinenfabrik Reinhausen Gebruder Scheubeck K.G., Regensburg, Germany Filed June 16, 1969, Ser. No. 834,245 Claims priority, application Germany, July 5, 1968, 1,763,623 Int. Cl. H021) 13/06; H02m 5/12 US. CI. 32.3-43.5 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF INVENTION Tap-changing transformer systems include three units, i.e. the transformer proper with a tapped winding, a selector switch for selecting the desired tap of the aforementioned winding and preparing its insertion into the circuit, and a transfer switch for performing tap-changing operations which means breaking current-carrying circuits and closing live circuits. Current limiters such as impedances or resistors form also an integral part of any transfer switch.

There are state-of-the-art transfer switches which include vacuum switch units for performing tap-changing operations. Vacuum switch units require high contact pressures, e.g. a vacuum switch unit having a high currentcarrying capacity may require a contact pressure in the order of 600 lbs. If a tap-changing switching operation is performed by a fast acting spring-motor as, for instance, in so-called Janssen-type transfer switches, high contact pressures of the aforementioned order greatly complicate the design of the transfer-switch-operating spring-motor. These complications are particularly troublesome in case of three-phase systems since the transfer switches of such systems call for a spring-motor capable of operating simultaneously the vacuum switch units of the three phases of a transfer switch.

It has been proposed to reduce the extremely onerous requirements imposed upon the spring-motor for operating a transfer switch including one or more vacuum switch units by providing a current-carrying shunting switch across each of the vacuum switch units of the transfer switch. While this expedient makes it possible to greatly reduce the contact pressure requirements of the vacuum switch unit, or the vacuum switch units, respectivley, of the transfer switch, it bars the use of standard type selector switches and calls for special selector switches, which is a highly undesirable limitation of tap-changing transformers including transfer switches of the aforementioned character.

The present invention avoids the limitations and drawbacks of the aforementioned tap-changing systems including transfer switches having vacuum switch units. To be more specific, this invention aims to greatly reduce the contact pressures required for the vacuum switch unit,

Patented Jan. 12, 1971 or the vacuum switch units, of the transfer switch without requiring special and relatively complex selector switches.

SUMMARY OF INVENTION A tap-changing transformer embodying this invention has a winding having at least one pair of contiguous taps. Such a transformer further includes a first changeover switch having a pair of fixed contacts each conductively connected to one of said pair of taps and a movable con tact selectively engageable with each of said pair of fixed contacts and an intermediate position separate from said pair of fixed contacts. The transformer further includes a second changeover switch having a pair of fixed contacts each conductively connected to one of said pair of taps and a movable contact selectively engageable with each of said pair of fixed contacts and having an intermediate position separate from said pair of fixed contacts. In addition to the above a tap-changing transformer embodying this invention includes a first vacuum switch unit and a second vacuum switch unit. The latter is connected in series with a resistor and both said second vacuum switch unit and said resistor are shunted across said first vacuum switch unit. A tap-changing transformer embodying this invention further includes conductor means for serially connecting said movable contact of said first changeover switch with said first vacuum switch unit and said second vacuum switch unit and conductor means for shunting said movable contact of said second changeover switch across said movable contact of said first changeover switch and said first vacuum switch unit and across said second vacuum switch unit and said resistor.

BRIEF DESCRIPTION OF DRAWINGS FIGS. 18 are circuit diagrams of tap-changing transformers and their tap-changing switching circuitry, the latter being shown in the several different positions thereof involved in a tap-changing operation;

FIG. 9 is a diagrammatic representation of the sequence of steps involved in a tap-changing operation; and

FIG. 10 is a diagrammatic representation of the same circuitry as FIGS. 1-8 and further shows a drive for operating the constituent switch means of the system.

DESCRIPTION OF PREFERRED EMBODIMENT OF INVENTION As mentioned above FIGS. 1 to 8, inclusive, illustrate the consecutive steps involved in a tap-changing operation in a system embodying the present invention. Reference character Tr has been applied to indicate a tapped winding of a transformer and reference character L has been applied to generally indicate a transfer switch for performing tap-changing operations. The conventional selector switch which forms a necessary part of the system has been deleted in FIGS. 1-8 since showing of such a switch is not necessary for an understanding of the present invention. A selector switch which may be added to the system of FIGS. 1-8 is fully disclosed in US. Pat. 3,176,- 089 to A. Bleibtreu, Mar. 30, 1965, for Load Tap Changers for Transformers and in US. Pat. 3,366,750 to A. Bleibtreu, Jan. 30, 1968, for Switching Mechanism for Tapped Regulating Transformers. The taps A and B of winding Tr may be considered as a pair of contacts of a selector switch conductively connected to two contiguous taps of winding Tr. The transfer switch L includes a pair of vacuum switch units C and D. The former is arranged in the main current path of transfer switch L and the latter is arranged in the auxiliary current path of transfer switch L in series with the switch over resistor R arranged in the aforementioned auxiliary current path. It will be apparent from FIG. 1 that the main current path including vacuum switch unit C and the auxiliary current path including vacuum switch unit D and switchover resistor R are arranged in parallel. Reference numerals E and F have been applied to indicate a pair of changeover switches. Each changeover switch E, F includes a pair of fixed contacts. One of the fixed contacts of changeover switch E is conductively connected to tap A of winding Tr and the other fixed contact of changeover switch E is conductively connected to tap B. In like fashion one of the fixed contacts of changeover switch F is conductively connected to tap A of tapped winding Tr and the other fixed contact of changeover switch F is conductively connected to tap B of winding Tr. Reference character Y has been applied to indicate an outgoing line. In the positions of changeover switches E, F shown in FIG. 1 the movable contact of current-carrying changeover switch E and lead b shunt both vacuum switch units C, D. The movable contact of changeover switch F and lead a are arranged in series with vacuum switch units C, D.

In the position of the parts of the system shown in FIG. 1 about one half of the current derived from tap A flows through current-carrying switch E to the outgoing line Y and about the other half of the current derived from tap A flows through closed vacuum switch unit Cto outgoing line Y.

A tap-changing operation from tap A to tap B is initiated by opening of changeover switch B so that neither of its fixed contacts is engaged by its movable contact. As a result, the entire load current supplied by the transformer is carried for a short period of time by vacuum switch unit C. This first step involved in a tap-changing operation has been illustrated in FIG. 2.

The next step in a tap-changing operation consists in engagement of the contacts of vacuum switch unit D, i.e. closing of the latter. This step involved in a tap-changing operation has been illustrated in FIG. 3.

Thereupon the contacts of the vacuum switch unit C are parted, i.e. the latter is being opened as shown in FIG. 4. The recovery voltage then appearing across vacuum switch C is substantially equal to the voltage drop across resistor R.

Now the movable contact of changeover switch E completes its travel from its right fixed contact to its left fixed contact, as shown in FIG. 5. Now vacuum switch unit D carries a current equal to the algebraic sum of the load current in outgoing line Y and a circulating current mainly determined by the voltage U between taps A and B and the magnitude of resistor R.

Thereupon the cooperating contacts of vacuum switch unit D part from each other as shown in FIG. 6. This completes the tap-changing operation from tap A to tap B.

Following completion of the tap-changing operation proper the movable contact of changeover switch F is moved from its left limit position shown in FIG. 6 to its right limit position shown in FIG. 7 and vacuum switch element C is reclosed as indicated in FIG. 8. Now the output current of the transformer is again substantially divided between changeover switch E and vacuum switch unit C. Thus a stationary condition has again been achieved, and now the load current is derived from tap B rather than from tap A.

It will be apparent from the foregoing that in the final position of the parts shown in FIG. 7 and in FIG. 8 about one-half of the load current flows through current-carrying changeover switch E, and about the other half of the load current flows through vacuum switch unit C. Thus the latter is required to carry but relatively limited currents, i.e. about one-half of the total load currents. This, in turn, makes it possible to reduce contact pressures and to shorten tap-changing switching times and to avoid complex spring-motor designs for effecting tap-changing operations.

FIG. 9 appears to be substantially self-explanatory in view of the foregoing description of FIGS. 1 to 8, inclusive. Each line D, E, F, C indicates the position of the switching devices D, E, F, C of FIGS. 1 to 8. The vertical 4 lines 1, 2, 3 6, 7, 8 of FIG. 8 refer to the points of time shown in FIGS. 1 to 8, inclusive.

FIG. 10 includes a diagrammatic representation of a common drive for the constituting switching devices C,

D, E, F of a tap-changing system embodying this invention. The positions of the switching devices C, D, E, F shown in FIG. 10 are the same as those shown in FIG. 1. Reference numeral 11 has been applied in FIG. 10 to indicate a shaft which may be pivoted in clockwise direction 'by motor means such as a powerful spring motor (not shown). Cams 12, 13, 14, 15 have different shapes and are fixedly mounted on shaft 11. Each cam controls a cam follower or roller. Thus cam 12 controls roller 16 which, in turn, controls operating rod 17 for vacuum switch unit C, cam 13 controls roller 18 which, in turn, controls operating rod 19 for vacuum switch unit D, cam 14 controls roller 20 which, in turn, controls operating rod 21 for pivoting the movable contact of changeover switch E, and cam 15 controls roller 22 which, in turn, controls operating rod 23 for pivoting the movable contact of changeover switch F. Operating rods 17, 19, 21, 23 may be biased in upward direction by spring means (not shown) to cause a precise determination of the positions of cam followers 16, 18, 20, 22 by the configuration of cams 12, 13, 14, 15.

If shaft- 11 is pivoted an angle of degrees the outgoing line Y is disconnected from tap A and connected to tap B. Speaking more generally, a pivotal motion of shaft 11 about an angle of 180 degrees results in a change from one tap to a contiguous tap of winding Tr. Assuming that the transformer winding Tr is provided not only with two taps but with a relatively large number of taps operatively related to a conventional selector switch, then each pivotal motion of shaft 11 about an angle of 180 degrees results in one of a plurality of successive tapchanging operations involving more than two taps. A close consideration of the shapes of cams 12, 13, 14, 15 reveals that their particular shape is conducive to the sequence of switching steps set forth in detail in connection with FIGS. 1 to 9, inclusive.

What I claim as my invention is:

1. A tap-changing transformer including (a) a tapped transformer winding (Tr) having at least one pair of contiguous taps (A, B);

(b) a pair of changeover switches (E, F) each having a pair of contacts and an additional contact movable relative to said pair of contacts and selectively engageable with each of said pair of contacts and selectively separable from each of said pair of contacts;

(0) conductor mean-s for conductively connecting each contact of said pair of contacts of each of said pair of changeover switches (E, F) with a different tap (A, B) of said pair of contiguous taps (A, B) of said transformer winding (Tr); and

(d) a transfer switch including a pair of parallel-connected vacuum switch units (C, D), one of said pair of vacuum switch units (D) being connected in series with a current-limiting resistor (R), each of said pair of vacuum switch units (C, D) being arranged to be conductively connected by the intermediary of said pair of changeover switches (E, F) to each of said pair of taps (A, B), one of said pair of changeover switches (F) being arranged to establish a current path in series with said pair of parallel connected vacuum switch units (C, D) and the other of said pair of changeover switches (E) being arranged to establish a current-path parallel to said pair of vacuum switch units (C, D).

2. A tap-changing transformer as specified in claim 1 including a common drive (11) for operating said pair of changeover switches (E, 'F) and said pair of vacuum switch units (C, D) in predetermined sequences.

3. A tap-changing transformer including (a) a tapped transformer winding (Tr) having at least one pair of contiguous taps (A, B);

(b) a first changeover switch (F) having a pair of fixed contacts each conductively connected to one of said pair of taps (A, B) and a movable contact selectively engageable with each of said pair of fixed contacts and having an intermediate position sepavacuum switch unit (C) from said one (A) of said pair of taps (A, B) to said outgoing line (Y);

(b) thereafter interrupting said first current path ('15, b) and maintaining said vacuum switch unit (C) in the closed position thereof;

rate from each of said pair of fixed contacts; 5 (c) thereafter establishing a shunt connection includ- (c) a second changeover switch (E) having a pair ing a resistor (R) and another vacuum switch unit of fixed contacts each conductively connected to one (D) in closed position thereof across said vacuum of said pair of taps (A, B) and a movable contact switch unit (C); selectively engageable with each of said pair of fixed 10 (d) thereafter opening said vacuum switch unit (C); contacts and having an intermediate position sepa- (e) thereafter establishing a direct current path (E, b) rate from each of said pair of fixed contacts; from the other (B) of said pair of taps (A, B) to (d) a first vacuum switch unit (C); said outgoing line (Y); (e) a second vacuum switch unit (D) connected in (f) thereafter opening said another vacuum switch unit series with a resistor (R), said second vacuum switch (D); and unit (D) and said resistor (R) being shunted across (g) thereafter establishing a current path (P, a) insaid first vacuum switch unit (C); cluding said vacuum switch unit (C) in the closed (f) conductor means (a) for serially connecting said position thereof from said other of said pair of taps movable contact of said first changeover switch (F) (B) to said outgoing line (Y). with said first vacuum switch unit (C) and said sec- 0nd vacuum switch unit (D); and References Clted (g) conductor means (b) for shunting said movable UN S A PA N contact of said second changeover switch (E) across said movable contact of said first changeover switch 10/1968 Breuer 323 43'5(X) (F) and across said first vacuum switch unit (C) FOREIGN PATENTS and across said second vacuum swltch unit (D) and Said resistor (R) 12,497 1964 Netherlands 323-435 4. A method for performing a tap-changing operation 1164782 1969 Great f f 32343-5 on a tapped transformer winding including at least one 1,172,312 1969 Great Bntam pair of contiguous taps, said method including the steps of (a) carrying current from one (A) of a contiguous J D MILLER Pnmary Exammer pair of taps (A, B) of a tapped transformer wind- G. GOLDBERG, Asssitant Examiner ing (Tr) by a first current path (E, b) to an out going line (Y) and simultaneously carrying current CLXR- by another parallel current path including a closed 336- 

